1. Field of the Invention
The present invention relates generally to a multi-layered golf ball having a core, a thin moisture vapor barrier layer, and an outer cover, wherein the moisture barrier layer is preferably made from a non-ionomeric polyolefin composition. The thickness of the moisture barrier layer is preferably in the range of 0.0001 to 0.010 inches. Preferably, the moisture barrier layer is applied by a powder coating or solution coating method.
2. Brief Review of the Related Art
Golf balls having solid inner cores made from a polybutadiene rubber material cross-linked with peroxide and/or zinc diacrylate are common in the industry. The inner core primarily provides resiliency to the golf ball. One problem with such golf balls is that water vapor may permeate into the cores and harmfully affect the core's properties. As the core absorbs water, it tends to lose its resiliency. The compression and coefficient of restitution (COR) of the ball may be reduced significantly as water enters the core.
The compression value of a golf ball or a golf ball subassembly (for example, golf ball core) is an important property affecting the ball's playing performance. For example, the compression of the core can affect the ball's spin rate off the driver as well as the “feel” of the ball as the club face makes impact with the ball. In general, balls with relatively low compression values have a softer feel. As disclosed in Jeff Dalton's Compression by Any Other Name, Science and Golf IV, Proceedings of the World Scientific Congress of Golf (Eric Thain ed., Routledge, 2002) (“J. Dalton”) several different methods can be used to measure compression including Atti compression, Riehle compression, load/deflection measurements at a variety of fixed loads and offsets, and effective modulus. For purposes of the present invention, “compression” refers to Atti compression and is measured according to a known procedure, using an Atti compression device, wherein a piston is used to compress a ball against a spring. The test methods for measuring compression of the ball in accordance with the present invention are described in further detail below.
The “coefficient of restitution” or “COR” of a golf ball means the ratio of a ball's rebound velocity to its initial incoming velocity when the ball is fired out of an air cannon into a rigid vertical plate. The COR for a golf ball is written as a decimal value between zero and one. A golf ball may have different COR values at different initial velocities. The United States Golf Association (USGA) sets limits on the initial velocity of the ball so one objective of golf ball manufacturers is to maximize the COR under these conditions. Balls with a higher rebound velocity have a higher COR value. Such golf balls rebound faster, retain more total energy when struck with a club, and have longer flight distance. In general, the COR of the ball will increase as the hardness of the ball is increased. The test methods for measuring compression of the ball in accordance with the present invention are described in further detail below.
The surface hardness of the golf ball is another significant property considered in ball design and construction. Surface hardness generally refers to the firmness of the ball. The test methods for measuring surface hardness of the ball in accordance with the present invention are described in further detail below.
The industry has attempted to address the problem of moisture penetrating into the core layer by applying a barrier layer over the core. The moisture vapor barrier layer encapsulates the core to protect it from the negative effects of moisture. Some materials for making moisture vapor barrier layers are described in the patent literature.
For example, Sullivan et al., U.S. Pat. No. 5,820,488 discloses golf balls having a solid inner core, an outer core, and a water vapor barrier layer disposed therebetween. The water vapor barrier layer preferably has a water vapor transmission rate lower than that of the cover layer. The water vapor barrier layer is formed from polyvinylidene chloride, vermiculite, or a barrier-forming material disposed on the core through an in situ reaction.
Feeney U.S. Pat. No. 6,232,389 discloses a barrier layer for an air or other gas-filled sports balls including golf balls. The barrier layer is formed from an aqueous solution of an elastomer, a dispersed exfoliated layered filler, and a surfactant.
Wai, U.S. Pat. No. 6,398,668 discloses golf balls having a polybutadiene core and an oxygen barrier layer disposed over the core. The barrier layer is made of an ethylene vinyl alcohol copolymer film.
Cavallaro et al., U.S. Pat. No. 6,632,147 and Hogge et al., U.S. Pat. No. 6,838,028 discloses golf balls having an intermediate moisture vapor barrier layer that may be made from (i) multi-layer thermoplastic films including polypropylene films, which have been metallized or coated with polyvinylidene chloride (PVDC), (ii) blends of ionomers, polyvinyl alcohol copolymer and polyamides, and (iii) dispersions of acid salts of polyetheramines, among others.
Hogge et al., U.S. Pat. No. 6,932,720 discloses golf balls having moisture vapor barrier layers made of butyl rubber. The butyl rubber may also be a halogenated butyl rubber such as bromobutyl rubber or chlorobutyl rubber. The butyl rubber may also be a sulfonated butyl rubber. The butyl rubber may be blended with other polymers, such as double bond-vulcanizable rubber, ethylene propylene diene monomer rubber and vinylidene chloride. The moisture barrier layer also may be formed from a composition comprising an elastomer, preferably in combination with a double-bond vulcanizable rubber. The elastomer may comprise at least a conjugated multi-olefin or an iso-olefin. The elastomer may be halogenated, sulfonated, or both. The elastomer may also comprise branched styrenic blocks.
Hogge et al., U.S. Pat. No. 7,004,854 discloses a golf ball having a core, intermediate barrier layer, and cover, wherein the barrier layer has a moisture vapor transmission rate lower than the cover. The barrier layer is formed of a thermoplastic or thermoset composition comprising microparticles, such as fibers, whiskers, metal flakes, micaceous particles, nanoparticles, or combinations thereof, dispersed in a binder comprising synthetic rubbers, natural rubbers, polyolefins, styrenic polymers, single-cite catalyzed polymers, or combinations thereof. The thickness of the barrier layer may be in the range of about 0.001 inches to about 0.01 inches.
Hogge et al., U.S. Pat. No. 7,182,702 discloses a golf ball having a moisture vapor barrier layer that is formed from a composition comprising an elastomer (for example, halogentated butyl rubber) and a double-bond vulcanizable rubber that is cured by infra red radiation or a combination of infra red and ultra violet radiation.
Jordan, U.S. Pat. No. 7,306,528 discloses a golf ball having a moisture vapor barrier layer comprising a blend of a non-ionomeric acid terpolymer (ethylene, a softening acrylate class ester such as methyl acrylate, n-butyl-acrylate or iso-butyl-acrylate, and a carboxylic acid such as acrylic acid or methacrylic acid) and a copolymer (ethylene and methacrylic acid). The '528 patent further discloses that Nucrel™ copolymers of ethylene and methacrylic acid (DuPont) can be used.
Hogge et al., U.S. Pat. No. 7,357,733 discloses moisture vapor barrier layers made from compositions comprising a filler dispersed in a liquid or solvent-borne elastomeric polymer of multi-olefin, iso-olefin, or a combination thereof. Suitable elastomers include brominated polymers derived from a copolymer of isobutylene (IB) and p-methylstyrene (PMS). A copolymer of isobutylene and isoprene with a styrene block copolymer branching agent also can be used.
Although the foregoing materials can provide an effective barrier to moisture penetration, they may need to be applied at relatively high thickness in order to do so. One problem with applying relatively thick layers of the material tom make the barrier layer is that this may cause other desirable properties of the golf ball to degrade. In other words, the relatively thick barrier layers may be effective in preventing moisture penetration, but this potential benefit can be offset by a loss in the ball's playing performance properties. For example, if the layer is too thick, it will contribute to the ball having reduced COR; hence, the ball will have reduced flight distance. Thus, it would be desirable to develop a golf ball having a moisture vapor barrier layer that can be applied thinly, that is at a thickness sufficient to prevent the penetration of moisture into the core, but that does not degrade the playing performance of the ball. The present invention provides golf balls having such characteristics as well as other advantageous properties, features, and benefits. The invention also encompasses methods for making such golf balls.